The present disclosure relates to the use of indole-3-propionic acid (hereinafter “IPA” or “I3PA”) as a therapeutic agent, as a protective agent against late onset of cardiovascular and neurodegenerative disease, and as a biomarker for disease and health conditions. The disclosure has particular utility in connection with neurodegenerative diseases such as Huntington Disease (HD), Alzheimer Disease (AD), Mild Cognitive Impairment (MCI), Lower Motor Neuron Disease (MND) including but not limited to Amyotrophic Lateral Sclerosis (ALS), Parkingson's Disease (PD) as well as hypertension, stroke and ischemic heart disease and head injury, and will be described in connection with such utilities, although other utilities are contemplated.
IPA is an indole produced in organisms such as c. Sporogenes that have the enzyme to remove the OH from the 2 position on the propionic acid side chain of indole lactic acid an end product of tryptophan metabolism in mammalian species. It is one of several gut metabolites that affect the plasma metabolome [12]. Other organisms such as brewers yeast also show the ability to produce IPA (See below a means of producing purified IPA preparations using brewers yeast or similar organisms). Current understanding is that IPA serves as an antioxidant whose intermediate indoxyl positive free radical, unlike such compounds as tocopherols and carotenes has no pro oxidant intermediates [11,14,15,17] and in vitro has been shown to suppress protein aggregation and suggested as a therapeutic for Alzheimer's Disease [13,16,18]. IPA also has been shown in culture studies to suppress other microbial species such as E. coli (Pauley et. al. Effect of Tryptophan analogs on depression of the Enchiridia Coli Tryptophan Operon by Indole 3 propionic Acid: Journal of Bacteriology 219-226 (1978). We have shown that in plasma IPA is strongly bound to plasma proteins both albumin and immunoglobulins with normal plasma levels of ca. 200 ng/ml and free levels of ca. 0.1 ng/ml. The loading capacity of plasma for IPA is approximately 10 ug/ml before significant additional loading shows linearity of free material with added material. In plasma loading studies IPA replaces other indoles such as 3 hydroxy kynurenine and 3 hydroxy anthranillic acid which are thought to have possible deleterious effects on protein. We have shown that on free radical attack the intermediate positive ion free radical binds to protein as a kynuric acid moiety. The displacement of other indoles, the strong coordinate binding to protein and the defense of the protein against free radical attack leaving a residue that does not lead to crosslinking and denaturation are mechanisms that provide protection and improve functionality of an organism. We have shown that IPA produced in the gut enters the plasma and crosses the BBB and is found in brain and CSF. Residual fecal levels are lower than plasma levels and indicate that the majority of IPA produced is transferred to plasma. Intra peritoneal injected IPA derivative such as the amide (IPAM) are rapidly converted to IPA in the plasma. We also have identified two metabolites of IPA that allow monitoring of levels in excretion samples such as urine which correlate with plasma and brain levels.
Many late onset illnesses of the CNS or cardiovascular system have characteristics of free radical damage reflected in reduction of protective agents such as tocopherols, ascorbate etc. and damage products of lipids proteins and DNA. Different approaches to controlling this aim at different structures and processes—Antioxidants such as CoQ10 to reduce DNA damage and protect mitochondrial function, selected lipid diets to reduce lipid oxidation, materials such as creatine to enhance energy efficiency and reduce free radical burden, ascorbate to provide general peripheral protection. CNS disorders such as MCI, AD and HD and to a more limited extent PD and ALS also involve protein aggregation-currently considered to be the proximal cause of neuronal death in Huntington's disease, Alzheimer's disease and other neurodegenerative disorders. Specific agents to prevent damage to proteins have not been as extensively studied. These commonalties in late onset disease lead to the concept that there is a failure of control of the biochemical system reflecting the interaction and feedback among the genome transcriptome, proteome metabolome environment and commensal gut microbiome. It is this failure of feedback that in fact is the disease and that leads eventually to the symptoms. Consequently one looks for places in the network where genetic or environmental changes have created a non lethal but sub optimal level of control. These nodes or compounds can then be evaluated as therapeutics or as risk factors that like cholesterol for instance can be modified to reset or reestablish control.
We have shown in animal models and in human studies that the individuals genome determines the aggregate composition of the commensal gut microbiome and consequently the levels of I3PA produced in the gut. I3PA levels are then to an extent an inherited characteristic and low levels that are present in neurodegenerative and cardiovascular disease constitute an inherited characteristic that place individuals at higher risk for these diseases. Increasing these levels by supplementation and/or by modification of the aggregate makeup of the commensal gut microbiome is thus and approach to reducing risk as well as a therapeutic approach to intervention when such risk has been realized in the development of symptoms of disease.